There is no official formal night on the three-night cruise. You are just supposed to dress up a little on the night you go to Triton's. For mostpeople, that seams to mean church-type or nice-restaurant-type dressing up, and some of the little girls wear Disney princess dresses. On both our cruises, we also saw people wearing formal clothes that night. They were definitely in the minority, but they did not look out of place either.